1. Field of the Invention
The present invention relates to a hard copy technique wherein coloring materials are arranged on an image receiving medium such as paper and the like according to image signals, and more particularly to a recording technique involved in a thermal transfer recording system.
2. Description of the Prior Art
Recently, attention has been drawn to a thermal transfer recording system of sublimation type which employs a thermal transfer sheet having a heat-resistant sheet-form substrate and an ink layer containing a sublimative dye, and an image receiving medium having a dye acceptor layer for receiving the dye as it is diffused thereinto by heating from the back of the thermal transfer sheet, since the system exhibits excellent medium tone-recording performance and provides full-color image records, as described in, for example, IEEE Transactions on Consumer Electronics, Vol. CE-28, No. 3, pp. 226-232, Aug. 1982, and Journal of Imaging Science, Vol. 35, No. 4, pp. 263-273, Aug. 1991.
With such a thermal transfer recording system of sublimation type, the process of recording is carried out in such a way that the ink layer on the thermal transfer sheet and the dye acceptor layer on the image receiving medium, as placed in superposed relation, are first heated by a thermal head from the sheet-form substrate side of the thermal transfer sheet according to a signal from a recording signal source. During this heating, dye is diffused into the dye acceptor layer from the ink layer in proportion to the quantity of heat applied so that subsequently when the thermal transfer sheet is separated from the image receiving medium, the dye acceptor layer will have a visible image formed therein by the diffusion-transferred dye.
A thermal transfer sheet for use with such thermal transfer recording system of sublimation type is constituted of a sheet-form substrate formed of a polyethylene terephthalate (PET) film or the like having a thickness of, for example, about 9 .mu.m, and an ink layer formed by a solvent coating method on the surface of the sheet-form substrate, the ink layer containing 10 parts by weight of a styrene acrylic resin as a binder and 6 parts by weight of a sublimating disperse-dye. An image receiving medium for use in such system is constituted of a base formed of, for example, polyester or wood free paper, and a dye acceptor layer of a polyester resin which is formed on the surface of the base.
However, the above described system, which is adapted for utilization of thermal diffusion of dye into the dye acceptor layer, has such disadvantage that the system is generally unable to effect recording on a pulp-based paper such as papeterie paper or postcard paper, that is, on an image receiving medium having no dye acceptor layer.